We have, then, on the one side, the fact before us that wherever we meet
in the animal kingdom with difference of shape, form, and construction,
so different as to constitute a class, a genus, or a family of its own,
there we meet at the same time with a distinct and specific scent and
smell. On the other hand, we know that these specific odours are
invariably interblended with the very life-blood of the animal. And
lastly, we know that these specific odours cannot be accounted for by
any agents taken up in the shape of food from the outer world. We are,
then, driven to the conclusion that they are properties of the inner
animal; that they, in other words, pertain to the specific protoplasm
of the animal concerned.
And thus our conclusion attains almost certainty, when we remember that
it stands the crucial test of experiment--that we need only decompose
the blood in order to find there what we contend to be an essential
ingredient of it.
I must now say a few words in explanation of the term protoplasm.
Protoplasm is a soft, gelatinous substance, transparent and homogeneous,
easily seen in large plant-cells; it may be compared to the white of an
egg.
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